A variety of techniques, including energy saving processes, high-efficiency power generation processes, renewable energy technologies, artificial forestation or biological processes, have been developed to attempt to reduce emissions of carbon dioxide (CO2), which is one of representative greenhouse gases. However, under the current situation in which there is a need for continuous industrial development while maintaining the industrial foundation, a carbon capture and storage (CCS) (Sequestration) technique is a process capable of reducing large amounts of carbon dioxide emissions within a short period. The CCS technique may be divided into a capture process and a storage process.
The capture process consists of a pre-combustion capture process, an oxy-combustion process, and a post-combustion capture process. In the pre-combustion capture process, a carbon-containing fuel is converted into carbon dioxide and a hydrogen fuel using an appropriate reaction (e.g., a modification reaction, water gas shift reaction, etc.), carbon dioxide is captured and removed for combustion, thereby fundamentally preventing carbon dioxide from being produced in a reaction product.
In the oxy-combustion process, an absolute amount of exhaust gases can be reduced using only the nitrogen-removed oxygen, rather than using air as an oxidizer of a fuel, and carbon dioxide can be easily isolated and removed from the exhaust gases including only carbon dioxide and water.
The post-combustion capture process is a technique for isolating carbon dioxide from the post-combusted exhaust gas is isolated and is advantageous in that it can be most easily applied to the existing carbon dioxide sources.
The technique for isolating carbon dioxide may include a sequestration method using an appropriate solvent (for example, an amine-based absorber), a sequestration method using a separator membrane and a sequestration method using carbon dioxide absorption and adsorption of solid particles.
The carbon dioxide, once captured in the aforementioned manners, should then be stored using appropriate methods. Currently, methods of storing carbon dioxide in the ground or deep sea are generally being studied. According to these methods, carbon dioxide being in a supercritical state is injected into the underground space, such as an oil reservoir, a gas reservoir or a saline layer and then undergoes thermodynamic, hydrodynamic and chemical behaviors for sequestration and storage. However, there is a risk of re-emission of the stored carbon dioxide into the atmosphere or seawater due to limitation in the underground storage space and leakage of supercritical-state carbon dioxide stored at a high pressure. If carbon dioxide leaks in seawater, the marine ecosystem may be adversely affected by ocean acidification.
Other methods for sequestration and storage of large amounts of carbon dioxide include ocean storage methods. The ocean storage methods include a method of directly injecting carbon dioxide into the seawater to a depth of 1,000 m or greater and dissolving the same in the ocean, and a method of injecting high-density liquid carbon dioxide obtained by liquefying the carbon dioxide using a compressing device into an underground isolated space to a depth of 3,000 m or greater. However, in a case where carbon dioxide is directly injected into the seawater and stored in the ocean, the marine ecosystem may be affected by ocean acidification and there may be a possibility of re-emission of the dissolved carbon dioxide ultimately being in balance with the air. Thus, the direct injection method may not be considered as permanent sequestration and storage method. In addition, the method of injecting high-density liquid carbon dioxide is disadvantageous in that equipment and power for ocean acidification and liquefying and equipment and power for transportation of liquid carbon dioxide are required.